The present invention relates to bearings for timepieces, more particularly of the type allowing shocks to be absorbed. The constructors of mechanical watches have, for a long time, been designing numerous devices which allow a staff to absorb the energy resulting from a shock, in particular a lateral shock, by abutment against a wall of the hole of the base block which it traverses, whilst allowing a momentary displacement of the small rod before it is returned to its lock position under the action of a spring.
FIGS. 1 and 2 illustrate a device termed inverted double cone which is currently used in timepieces found on the market.
A support 1, the base of which comprises a hole 2 for the passage of the balance staff 3 ended by a small rod 3a, makes it possible to position a jewelled bearing 20 in which there are immobilised a pierced stone 4 traversed by the small rod 3a and a counter-pivot stone 5. The jewelled bearing 20 is retained in a housing 6 of the support 1 by a spring 10 which, in this example, comprises radial extensions 9 which compress the counter-pivot stone 5. The support 1 is a part of revolution comprising a circular rim 11. This rim 11 is interrupted at two places which are diametrically opposite by an opening 10 so as to create two semi-circular rims 11a, 11b. The opening 12 is provided in part in the two semi-circular rims 11a, 11b so as to produce two returns 13. The jewelled bearing 20 is retained in a housing 6 of the support 1 by elastic means, such as a spring 10, which comprises, in this example, radial extensions 9 which compress the counter-pivot stone 5. The spring 10 is of the axial type and has the shape of a lyre designed to be supported under the returns of the semi-circular rims 11a, 11b. The housing 6 comprises two bearing surfaces 7, 7a in the form of inverted cones on which complementary bearing surfaces 8, 8a of the jewelled bearing 20 are supported, said bearing surfaces requiring to be produced with very great precision. In the case of axial shock, the pierced stone 4, the counter-pivot stone 5 and the balance staff are displaced and the spring 10 acts alone to return the balance staff 3 into its initial position. The spring 10 is dimensioned to have a displacement limit so that, beyond this limit, the balance staff 3 comes into contact with stops 14 making it possible for said staff 3 to absorb the shock, which the small rods 3a of the staff 3 cannot do without the risk of breaking. In the case of lateral shock, i.e. when the end of the small rod unbalances the jewelled bearing 20 out of its lock plane, the spring 10 cooperates with the complementary inclined planes 7, 7a; 8, 8a in order to re-centre the jewelled bearing 20. Such bearings have been sold for example under the trademark Incabloc®. These springs can be produced in chromium-cobalt alloy or brass and are manufactured by traditional cutting means.
Now, a disadvantage of these shock-absorber systems is that their assembly is not easy. In fact some parts, such as the support 1 and the spring 10, must be orientated and manipulated in a certain manner during the assembly operation in order that the assembly can take place. Hence, the assembly of the shock-absorber system begins by being provided with a support, then a jewelled bearing with these stones. The latter is placed in the housing of the support. Then a spring of the axial type is provided, which has the shape of a lyre. The latter is manipulated so that it can be supported under the returns of the semi-circular rims 11a, 11b of the support.
Consequently, positioning the spring and fixing it to the support requires a specific manipulation. For this reason, shock-absorber systems must be assembled in part manually because a robot cannot produce such a complex manipulation.
Furthermore, the current shock-absorber systems are assembled in part manually and not by a robot because human beings are capable of knowing immediately the orientation in which the parts of the shock-absorber system must be placed relative to each other. In fact whatever the shape of the parts, human beings are able to know immediately how they must manipulate these parts in order to assembly them. Now, even if a robot can distinguish the orientation of one piece relative to another, this requires a more complex and more expensive robot whilst requiring more time. This reduces consequently the manufacturing output.
Hence, total automation of the assembly is not possible and the assembly process of the shock-absorber systems is therefore more expensive.